Conventionally, wire bonding has been frequently used for connection between a substrate and an external connecting terminal in power semiconductor modules.
In recent years, there is a request for an apparatus in which a drive device and a control device are integrated, that is, a mechanically and electrically integrated apparatus in order to obtain an increase in capacity, size reduction, power loss reduction, noise reduction, and further reduction of the number of parts. In the mechanically and electrically integrated apparatus, a relay terminal is used instead of wire bonding.
However, current flowing in the relay terminal increases along with the increase in capacity, and a heat generation amount increases on the other hand. Thus, a difference in thermal expansion between the substrate and the relay terminal is caused and stress on a soldering section is generated, and there is a concern of reduction in service life of a solder.
There is a known technique that mitigates stress to be applied to a soldering section by using a copper material subjected to annealing in advance as a relay terminal, and employing a bend structure in a lower part in order to improve service life of a solder between the relay terminal and the soldering section (for example, see PTL 1).
In addition, there is a known technique that reduces damage according to repetition of a temperature cycle of a soldering section and improves durability by soldering a first layer, made of a first material having a thermal expansion coefficient approximating to that of a substrate, to the substrate in order to improve service life of the solder between a relay terminal and the soldering section (for example, see PTL 2).